This invention relates to optical location tracking devices. More specifically, this invention relates to devices using optical detectors to determine the locations of light sources.
Heretofore, a variety of optical location tracking devices have been built. U.S. Pat. No. 4,558,313 describes a location indicator using a scanning light beam. The location of an object is detected when the object blocks a scanning light beam. This type location tracking system comprises complex mechanical apparatus to generate a scanning light beam. The input device of the system must locate in a pre-defined narrow region. Any foreign object blocks the scanning light beam by accident will cause false interpretation. Its supporting electrical circuit is also complex. U.S. Pat. No. 5,166,668, U.S. Pat. No. 5,159,322, and U.S. Pat. No. 4,782,328 describe systems using an array of closely spaced optical sensors such as charge coupled devices (CCD) to determine the location of a light source. This type of location tracking systems must use a large number of closely spaced light sensors. A complex system is required to obtain information from a large number of sensors. The data analysis procedure is also complex. Another type of optical tracking devices are the sun tracking devices designed to aim a solar panel to face the sun. Two examples of sun tracking devices are described in U.S. Pat. No. 4,225,781 and U.S. Pat. No. 3,268,185. Those sun tracking devices are able to determine whether the solar panels are off target or not, but they are not able to do accurate location measurement for a point source. U.K. Pat. No. 2,232,550 describes a direction-of-arrival sensor (DOAS) using four mirrors and four sensors to determine the incident angle of a collimated light beam. The DOAS device is fragile because it requires perfect reflectors that are arranged perfectly perpendicular to one another. It won't be able to tolerate dust or mist existed in practical operation conditions. U.S. Pat. No. 4,550,250 describes a location tracking device that only requires a small number of light sensors. The light emitted from a light source is confined by a vertical slit to form a line-shaped bright area. This line-shaped bright area falls on two light sensors with apertures of different shapes. The light incident angle is determined by measuring the ratio of the light intensities detected by those two light sensors. Those two light sensors must have uniform sensitivity at different locations for this device to be accurate. The light intensities in the line-shaped bright area also need to be uniform. Both requirements are not easy to achieve. The slit also limits available range and resolution of the system. All of the above optical location tracking systems are too complex to compete with existing commercial devices in terms of cost to performance considerations. They also tend to have reliability problems. It is desirable to have an optical location tacking device that can be manufactured with a cost-efficient process. It is also desirable to have a device that does not use any delicate component so that it can be reliable at normal operation conditions.